1. Field of the Invention
The present invention relates to a transmission apparatus, and more particularly, to a transmission apparatus which accommodates an asynchronous network and a SONET/SDH network.
2. Description of the Related Art
As a conventional transmission network, a synchronous network under a SONET/SDH scheme specified in SONET (Synchronous Optical Network) which is an ANSI (American National Standards Institute) standard or in SDH (Synchronous Digital Hierarchy) of ITU Recommendation is widely used. Data transmission over this SONET/SDH network secures a congestion-free fixed bandwidth. On the other hand, with the widespread use of the Internet in recent years, there is a growing trend to convert telephone voice data to IP (Internet Protocol) packets and transmit the data asynchronously through a router, that is, “IP implementation” and there is a growing demand for this packet transmission over a transmission network. Therefore, a router function is being incorporated into a transmission apparatus which accommodates a SONET/SDH network.
FIG. 16 is a block diagram showing a configuration of a conventional transmission apparatus.
A transmission apparatus 900 shown in FIG. 16 is constructed of an IP router section 910 which transmits an IP packet and a SONET ADM (Add Drop Multiplexer) 920 which switches between SONET frames. The IP router section 910 is provided with a switch, that is, a packet switch system (Packet Switch System) 911 which switches paths and a packet processing section (Packet Processing) 912 and the SONET ADM 920 is provided with a switch system (Switch System) 921 and a line interface (Line Interface) 922. This transmission apparatus 900 can switch both SONET frame format data and packet format data. However, in the transmission apparatus 900, a switch function is provided for each of the IP router section 910 and SONET ADM 920, and the switch function is required to achieve commonality from the standpoint of efficiency. To allow commonality of the switch function here, there may be a method of performing switching after converting SONET frame format data to a packet format. However, packet switching cannot avoid fluctuations in a transmission time and data buffering is required to absorb these fluctuations. Therefore, it is difficult to realize a large-capacity transmission apparatus because the problem of delays due to buffering becomes serious with such a transmission apparatus.
Here, National Publication of International Patent Application No. 2004-519123 discloses a scheme whereby packet format data is mapped to a time division multiplexing frame format which is defined by SONET and data in respective time division multiplexing, packet and ATM (Asynchronous Transfer Mode) formats are thereby switched using a common switch function.
However, the scheme described in National Publication of International Patent Application No. 2004-519123 subdivides packet data into 52-byte fixed length frames as defined in ATM and then performs mapping, and loss is thereby produced due to overhead generated every 52-byte fixed length frame and insertion of data to fill the blanks of fixed length frames, which suppresses transmission bandwidths.
The present invention has been made in view of the above circumstances and provides a transmission apparatus which suppresses transmission loss.